Snowmobiles are generally composed of a main frame which carries the engine, the operator's station, and the control mechanisms for the snowmobile. Positioned on the forward end of the snowmobile is a pair of snow engaging skis that may be steered for turning the snowmobile. The rear portion of the snowmobile carries the drive mechanism for the snowmobile which is generally composed of continuous belts driven by sprockets. Normally, there are three belt sections that make up the belt drive. They are a central belt, generally wider than the others, and two relatively narrow outer belts. The outer surfaces of the belts carry snow engaging lugs which cause the snowmobile to move when the belts are driven. The outer belts have their inner edges spaced from the outer edges of the central belt. The three belts are connected by what is commonly known in the trade as grouser bars. The grouser bars are conventionally metal bars that extend substantially the full width of the three belts and have portions thereof which extend between the gaps or grooves between the inner and outer belts. There is provided on the snowmobile a pair of guide rails that extend fore-and-aft of the machine. The guide rails face downwardly to engage the upper surfaces of the grouser bars in the gaps between the respective belts. The grouser bars have, as viewed in cross-section, a flat main bar portion with outwardly extending flanges at the front and rear edges of the bar portions.
One of the problems that exists with respect to the present type of belt structure that uses grouser bars is that the grouser bars are relatively stiff in the transverse direction and consequently, a stone or foreign object that may come into contact with the underside of the belt along one edge of the belt will tend to lift one side of the snowmobile. In some instances, if it is great enough, the stone or foreign object may even turn the snowmobile over to its side. Also, in some instances, the transverse flanges on the grouser bars tend to operate to steer or guide the entire snowmobile in a transverse direction. The grouser bar flanges may bite into the snow or ice and tend to turn or slide the snowmobile to one side. In many instances, this is an undesireable characteristic. This is particularly so when the entire length of the grouser bar is rigid and not flexible.
With the above in mind, it is the primary object of the present invention to provide a belt structure for a snowmobile, somewhat similar to that above described, but having incorporated in each grouser bar flex points or flex areas. Such flex points or areas may be created merely by cutting away a portion of the respective flanges at the front and rear edges of the grouser bars. The advantage of having such flex points occur upon the belt structure passing over a stone or other foreign object. In such an instance, the stone or foreign object might raise one side of the unit, but since the belt flexes at its flex point, the belt structure would yield in this area. Consequently, there would be less tendency for a stone or foreign object to tilt the snowmobile to a point where it turns over.
It is also an object of the present invention to provide transversely elongated lugs on the outer surfaces of the respective belts that will be in leading but close relation to the grouser bars and will extend across the area where the flex points exist on the grouser bars. The lugs will afford stiffness of the belts in the area of the flex points on the grouser bars. Consequently, the lugs will tend to eliminate constant flexing of the belt at those points as compared to bending when a large foreign object contacts one side of the belt structure. This, of course, will lead to a longer life of the grouser bar as well as the entire belt structure. It is further proposed to have the vertical length or depth of the lugs to be greater than the vertical length or depth of the flanges on the grouser bars. This will tend to eliminate the slicing or cutting action of the grouser bars as they contact the ground and to further eliminate the tendency of the snowmobile to accelerate in its movement in a transverse direction when it begins to slide from one side or the other.